In harsh ionizing radiation environments, charges can be trapped in various oxide regions in MOS transistors of integrated circuits. The radiation induced charge buildup can cause failure by shifting threshold voltages of MOS transistors and by creating deleterious leakage paths. These effects are especially harmful in thick oxides such as the field oxide (FOX), shallow trench isolation (STI) refilled oxide, and buried oxide (BOX) in devices fabricated in silicon-on-insulator (SOI) material. The net radiation-induced charge is usually found to be positive, causing a negative shift in threshold voltage.
Chemical treatment of these oxides has been found to be effective in reducing the radiation induced charge buildup. Examples of chemically treated films are treated gate oxides with excess silicon or shallow trench and field oxides prepared with boron and phosphorus doping, which is referred to as borophosphosilicate glass (BPSG). Reduction of the charge buildup by chemical treatment of these oxides can be attributed at least partially to electron trapping, which compensates for some of the positive trapped charges.